In my last post I wrote about the debatable merits of praying mantids, most of which aren't native insects and are indiscriminate eaters of other bugs. Since then I've been doing some digging on the other insects we most commonly consider "good" and want to attract to our gardens, and found a lot of interesting information.

The ladybug is a welcome sight in any garden, ravishing aphid-encrusted flower buds or tender vegetable crops. But if you're over the age of 25, these aren't the ladybugs of your childhood. The rosy red nine-spotted ladybug I remember, as well as many of the other 450 native species, has been almost eradicated by the Asian lady beetle, Harmonia axyridis, which has gained purchase in America in the last decade. These are the ladybugs that find their way into homes in large numbers in the fall, looking for a warm spot to overwinter.

The orange-red round beetles have decreased native ladybug populations not just by encroaching on habitat or stealing food; they have also been found to be carriers of a tiny parasite that their hyperactive immune system renders harmless, but is deadly to native ladybugs. The Asian lady beetle is a huge consumer of aphids and other plant parasite insects, so it's an effective biological weapon against pests. But it has upset the population of native species, and many entomologists feel that the species will continue to be dominant, causing a great reduction in ladybug biodiversity.

In this case as in others, the insects were intentionally introduced by the government. In the 1970s the Department of Agriculture released mass numbers of a variety of non-native ladybugs to see which species would survive and adapt. They all did, and are now found in even the most remote regions of the U.S.

Will there be unintended consequences if in ten years the country is populated by the same ladybug biomass, but made up of all exotic species? We don't know, of course. Insects are by far the most populous type of animal, but relatively few types have been studied, and the complexity and interdependence of their interactions is still an unknown.

But the idea that we can improve millions of years of evolution by salting the environment with foreign species has proven repeatedly to be a bad idea. Maybe the next generation of scientists will remember this.

Next week: Killer bees! Scary! But probably not in Philly.